Detailed transcriptional maps and translational maps of selected portions of the vaccinia virus genome were constructed. More than 12 early transcripts were characterized and two early genes were sequenced. These studies revealed that early mRNAs are colinear with the genome, unspliced, and have multiple closely spaced 5' ends. The nucleotide sequences for about 60 base pairs upstream of transcriptional initiation sites are extremely A T rich and contain long runs of As and Ts with some homology to prokaryotic and eukaryotic consensus sequences. The eukaryotic A2TA3 poly(A) signal sequence was not found near the ends of the genes. Marker rescue techniques were developed to map functional vaccinia virus genes. In this manner, thymidine kinase was mapped to the HindIII J fragment located near the center of the DNA molecule.